The invention pertains to an electropneumatic door control system for use on public transportation vehicles serving the transport of passengers, as for example buses. The controls are usually pneumatically or electropneumatically actuated, i. e. the driver triggers, for the purpose of opening or closing the door, a pneumatic or electropneumatic pulse which applies compressed air via a door valve in the form of a control valve to a door drive designed as door cylinder, and where the stroke movements of the door cylinder piston initiate the opening and closing of the door.
Since the most varied operating conditions have to be taken into account, particularly also mishandling by the passengers, the control must meet a number of marginal conditions. It is therefore a general demand, for example, that the closing motion of a pneumatically operated vehicle door automatically changes into an opening motion in the event that persons or objects are being squeezed in a closing door (reversing). The same applies for aggravated operating conditions which might occur, for instance, during the winter semester when the kinematics of the door change due to lower temperatures and when the closing motion of the door might be impeded as a result of snow or ice clumps. Due to the fact that even with the opening motion there is a danger that persons or objects get stuck, it is furthermore common practice to provide such a device for opening doors as well. In this instance, an electropneumatic switching arrangement merely causes the door to stop by a pressure release in the system, since here a reversal of the door motion would present a hazard for the people going through the door next.
A door control of this type was proposed, for example, in the German patent application No. P 30 32 516 (U.S. assignee's U.S. copending application Ser. No. 295,393) U.S. application has matured into U.S. Pat. No. 4,478,131. The system described there is provided with several electrical limit switches as well as electropneumatic differential pressure switches for the purpose of sensing the door positions and door behavior, e.g. meeting with obstacles. As is the case with all mechanical parts, these switches are subject to wear and tear. And furthermore, the mounting and adjustment of the limit switches as well as the pressure regulation for the differential pressure switches presents problems.
It is further known (DE-OS No. 30 03 877) to monitor the movement of the vehicle doors by presetting certain time intervals within which the closing or opening door should have reached a certain position. In this case the individual positions of the door are being scanned by reed switches or light barriers. If, due to some type of catch, the door does not reach one of these positions within the proper time, then the reversal procedure is triggered or the movement halted. The respective comparison between door position and time elapsed is executed in an electronic system which is in a discrete logic pattern and essentially contains timing elements.
One of the disadvantages of this known door control lies in the fact that relatively many reed switches or light barriers are required if a quick reaction of the reversal in all positions is to take place during the stroke of the door. Should the sensing of the door movement be too rough, as can occur when the distance between the sensing devices is large, then a relatively long time elapses until the reversal takes place, if in the most unfavorable case a door wing is being obstructed at the beginning of a monitoring period. Although this may be improved by increasing the number of reed switches or light barriers. However, this increases the cost for these components and also for the correspondingly higher number of timing elements within the electronic system. And furthermore, the expenditure is considerable which is required for the time adjustment of the timing elements for non-linear door movements.
Another disadvantage is that after the timing elements have been regulated the standard movement of the door wings is fixed and does not adapt to the changing operating conditions occurring in practical application. During the winter months, for example, as a result of the changed kinematics of the door they might have such an effect that the actual movement is slowed down as compared to the standard motion. A slower movement might also occur after the emergency cock has been actuated when the system is repressurized at a throttled pace.